[TCML] MOT shunts (was Capacitor Configuration)
cn at q.com
Sun Mar 20 15:11:23 MST 2011
If you can draw a vacuum on your oil tank, it will help. Breakdown
starts in small air pockets near the secondary winding, and if you can
evacuate to a good forepump vacuum, when the atmospheric pressure comes
back it will fill these voids with oil. This may not be the great
secret, but it should help. Be careful your tank doesn't implode.
Also, like Dr. R says, a filter is absolutely necessary. And it will
help to run the stack with the center tap grounded, like an nst.
> The insulation is breaking down due to harsh spikes.
> Even MOTs need a protective filter on the HV side just like nsts and even
> pole xmfrs.
> When you run two secondaries in series you are already stressing the
> insulation well beyond its design. Allowing harsh HV spikes into the sec
> coils makes this even worse, almost inviting a breakdown even if the xmfr is
> run in oil.
> Dr. Resonance
> On Sat, Mar 19, 2011 at 9:01 PM, Scott Bogard<sdbogard at gmail.com> wrote:
>> Hi Team,
>> I can add some to this, as I've killed a lot of MOTs in my time and
>> seem to have finally figured it out (a lot of mots, like 30+...) Using a
>> ballast is everything when stacking them, and I'll wager the better the
>> ballast the better the life expectancy. When running unballasted, I
>> immediately kill MOTs when I use more than 2 oil or not, I believe it is
>> because the unregulated current draw of 6 or 8 or 12 or whatever thousand
>> volts is too much to handle, the shunts probably exaggerate the heating
>> effect of the excess current, not to mention disfiguring the already
>> saturated magnetic flux... The only exception to this was when I ran SRSG,
>> and my small cap for my system limited my current, then oil made no
>> difference, they were impossible to kill but my results were lousy. I
>> theorize in countries where they use 240 V this is substantially less of an
>> issue, as for the same wattage output they use half the current through the
>> primary so they can double the wattage before MOT lethal current happens,
>> thus Peter Terren can run 4 mots unballasted with no trouble, and get 8 foot
>> sparks. Point blank, at the end of the day, after the fat lady has sung,
>> there is only so much you can get out of MOTs, and if you exceed that limit
>> they die, the trick is to make the best use of available power for good
>> results, the 240V guys will always have a leg up on us for this reason; for
>> me I will stick with just two, they are bullet proof like this even using no
>> oil, until your primary strikes kill them by breaking down the insulation,
>> as was the case on the last several I murdered. Just my two cents.
>> Scott Bogard.
>> On second thought, if you ran only 60 volts per primary and used more than
>> double the MOTS, you might be able to spread out the heat and reduce
>> saturation enough to get away with more than 4000V (like 6 MOTS for 6kV) I
>> think I might try this, under oil of course...
>> On 3/19/2011 4:40 PM, Jon Danniken wrote:
>>> John S. wrote:
>>>> I destroyed 8 MOTs before I realized the
>>>> secret....take the shunts out and make a good ballast. Removing the
>>>> shunts made the MOTs run much cooler. In fact, with them in, the oil
>>>> would be hot to the touch just after a few quick minute long runs. I
>>>> think that the heat contributed to their failure. Now I can run the
>>>> coil much longer and the oil never gets warmer than ambient temp. I
>>>> haven't lost a transformer since.
>>> Interesting observations, John. MOT shunts are one area where nobody
>>> really seems to be in agreement, at least from I have noticed over the
>>> last decade or so on the list. I have read some suggesting to leave them
>>> in, some suggesting to take them out, and some saying that it really
>>> doesn't matter.
>>> I do know that they are not anywhere near as significant as in an NST,
>>> but considering the intended application of a MOT as only running in a
>>> half-wave double, they don't need to be.
>>> What voltage were you running your MOTs at initially, when they were
>>> burning out? Do you think that perhaps running them with an external
>>> ballast had more of an effect than removing the shunts (ie, what was the
>>> voltage/current at each MOT before and after ballasting)?
>>> It would be nice to nail down the issue of MOT shunts once and for all
>>> and determine the best choice when using them in a TC supply. I've got a
>>> MOT I'll run some experiments with and publish the data when I am done.
>>> Tesla mailing list
>>> Tesla at pupman.com
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